Rated 5 out of 5 stars
Thanks a lot for this useful add-on!
One note though:
In v0.3.0, the "Digitally sign messages (by default)" flag seems to be stored with each identity but not evaluated when composing a new message using any of the defined identities.
Might be related to (or even caused by) the fact that I also use the "Virtual identities" add-on. I hope you can reproduce this error on your system.
(my e-mail address: my mozilla.org nickname at numlock dot ch)
This plugin only changes the configuration-dialog, nothing else. Thus the reason for "Digitally sign messages (by default)" not working has to be somewhere else. (For me it's working like a charme.)